Portable hot-air blower

ABSTRACT

A portable hot-air blower for at least two of the three forms of energy including oil, liquid-petroleum-gas, and electricity has a tubular or tunnel-shaped housing defining a combustion chamber and a blower in the housing including a fan and a fan motor for directing a current of air along an axis through the chamber. At least two heat sources are axially spaced in the chamber in the housing from one another. One of the heat sources is powerable by electricity and the other of the heat sources by a respective one of the other two forms of energy, that is oil or gas. An ambient-temperature sensor is connected to a controller that serves, on detecting a very low ambient temperature, to first operate the electrically powered heat source until the blower is warm enough for safe operation of the other heat source, and then start the other heat source.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US national phase of PCT applicationPCT/EP96/00800 filed Mar. 1, 1996 with a claim to the priority of Germanapplication 195 08 324.5 itself filed Mar. 9, 1995.

FIELD OF THE INVENTION

The invention relates to a portable hot-air blower for at least two ofthe three forms of energy--oil (also diesel and fuel oil),liquid-petroleum gas, and electricity--with a tubular or tunnel-shapedhousing.

Portable heaters of the described type have hitherto only been set upfor one of the three forms of energy. In them the motor for driving theblower moving the air is always electrically powered. Such portablehot-air blowers are used generally in construction, in farming, forthawing, tempering, and for frost protection of pipes and equipment aswell as emergency heaters. The main requirements of such a portablehot-air blower are the greatest possible mobility, the smallest size,and the lightest weight as well as the possibility of use in manyapplications.

Heaters for more than one form of energy are known for stationary use.Thus there are stoves, hot-air furnaces, cooking vessels, heaters, heatexchangers, and hot water heaters with devices for the alternate orsimultaneous use of different forms of energy.

German published application 3,236,242 describes for example a fan-lessspace heater for solid fuel which is provided for augmenting the heatoutput with electrical heating elements that can be used alone duringtransitional times for space heating.

A retrofit electrical heater for water heaters using solid or liquidfuel is further known from German utility model 7,419,316.

A stationary ventilator-assisted heating element is furthermore knownfrom German utility model 9,319,704 which is formed of a hot-water andnight-current storage element and/or heatable ceramic plates.

The above-described known devices do not meet the requirements withrespective to safety, venting, environmental concerns, size, and weightof the known portable hot-air blowers.

Portable hot-air blowers with low weight and which can easily be carriedor moved are only known to date for one of the three energy forms. Withthem the motor for moving the required amount of air is alwayselectrically powered. Such portable hot-air blowers are used in manyapplications, in agriculture, to thaw, warm, and prevent from freezingpipes and equipment and as emergency heaters. The requirements for sucha hot-air blower are the greatest possible portability, the smallestsize, and the smallest weight as well as many applications of use. Thesehot-air blowers have a tubular or tunnel-shaped construction.

Since the hot-air blowers of the known type are only set up for one formof energy they are burdened with energy-specific disadvantages. Thusoil-fired devices are the most effective with respect to energy costs;but their use for devices without heat-exchangers and venting is limitedto well vented spaces. As a result of the mixing of the exhaust gaseswith the room air the known hot-air blowers are in particular notsuitable for heating spaces in which men, animals, or plants remain.

The hot-air blowers fired with liquid-petroleum gas on the other handare more expensive with respect to energy and require--like oilheaters--good venting of the space being heated. They increase humidityand cannot be used below ground. Nonetheless, men, animals, and plantscan be exposed for long periods in rooms heated with liquid-petroleumgas.

Electrically powered hot-air blowers have no requirements with respectto venting; they are best suited for long-term exposure of men, animals,and plants. Since with electrically powered hot-air blowers no flamemust be ignited they also start at very low temperatures and under anyatmospheric conditions. Alone of the three groups of hot-air blowers theelectrically powered hot-air blowers can be used with great operationalsafety over the long term since electricity is always available toproduce heat energy so that shutdowns--as necessary for the periodicallynecessary refilling of oil heaters or for the exchange of gas bottlesfor gas heaters along with the associated requirements on servicepersonnel--do not occur. As a result of there being no need to vent thespace the energy requirements for a particular temperature level can besomewhat less than with the use of heaters with oil or gas; this isoutweighed however slightly by the cost of electricity per kWh comparedto oil and gas.

If one wants to take into account for example all the inside use orother commercial use with the changing applications of all use- andsafety-relevant, humanitarian, and locally required safetyconsiderations, the heater must not only meet the necessary spectrum ofapplication but must also be able to switch between the three energyforms. This requirement can nowadays only be met when at least for partsof the application spectrum oil and also gas and further electricalsystems are provided. The necessary capital investment results in acompromise not only with respect to the appropriateness of applicationbut also with respect to safety and humanitarian requirements. Even whenthe appropriate devices are stocked by the business the devices are usedin the field inappropriately as the appropriate device is notimmediately available at the location. For example if a painter wants toheat an above-ground room of a residence with a liquid-petroleum gasheater, he or she then takes it down to the cellar where only anelectrical heater is allowed.

OBJECT OF THE INVENTION

It is an object of the invention to reduce the volume, weight, andoverall expense for the portable-heater inventory of a business, to usea heater according to requirements with the energy best suited for theapplication selected from two energy forms, to reduce energy costs byrapid and simple conversion to another form of energy, and to increasethe service life--by automatic switching to the second or third energyform--while increasing safety.

SUMMARY OF THE INVENTION

This object is achieved in the described type of hot-air blower wherein

the housing is tubular or tunnel-shaped,

the energy converters are axially arranged in a common combustionchamber,

a jointly used blower having at least a fan and a fan motor is provided.

According to the invention the energy converters are connected to acontroller by means of which the energy converters, such as an oilburner, gas burner, and/or electrical heating element, are started orstopped. This starting can take place manually as well as automatically.As a result depending on nominal heat requirements more than one of theprovided energy forms can be used simultaneously. In a hot-air blowerprovided with heating elements using electricity and liquid-petroleumgas it is possible for example by switching on the electrical heatingelement to increase the loading of the electrical system and thus theefficiency of the overall apparatus when during use of the hot-airblower with liquid-petroleum gas the auxiliary energy for the fan, thecontroller, and the ignition is taken not from line but from anelectrical system operating at partial load.

In accordance with a further feature of the invention the controller isso constructed that in case of a disturbance in the selected mode ofoperation--for example failure of the gas or oil supply--it switchesautomatically over to the other form of energy or one of the other formsof energy. In the described hot-air blower with a gas-heater controller,the switch for a failure lamp can also serve for switching on theelectrical heating element when the controller shuts off the gas systembecause of lack of fuel or failure to ignite. With a hot-air blower ofthe described type with a nominal heat capacity of for example 10 kWwhen powered by liquid-petroleum gas, the fan motor, solenoid valve, andother electrical parts are normally powered from line which has anelectrical capacity of between 2 kW and 3.6 kW. The operation of theelectrical heating element of this hot-air blower can thus be undertakenwithout setting up a new electrical supply in this range, which in mostcases is sufficient for emergency operation, in particular to avoidfreezing. With this operation the same apparatus can therefore work as asimple electrical heater, for example in garages, cellars, and otherrooms below grade where oil and gas heaters should not be used.

A particularly advantageous embodiment of the object of the invention isthat the controller is connected with the fan motor and on switchover ofenergy type changes the rotation rate of the fan motor for the airthroughput appropriate to the respective mode of operation. In thismanner for each mode of operation the optimal amount of air is used byselection of the appropriate rotation rate of the fan motor.

The hot-air blower according to the invention can also be improved inthat the controller is constructed such that in case of a very lowambient temperature and/or disadvantageous weather conditions theselected mode of operation is started only when sufficient warmth hasbeen produced by the electrical heat element for a safe ignition of theappropriate energy converter. This preheating can take placeautomatically, for example by means of a thermostat or by manualoperation of a switch.

A further improvement of the hot-air blower according to the inventionis achieved in that the necessary switching, controlling, monitoring,and safety elements--with the exception of the energy-specificelements--are connected with all of the provided energy converters. Ahot-air blower constructed in this way necessitates only a modest extraproduction cost and can be made extremely compact. Thus with a hot-airblower using electricity and liquid-petroleum gas the only parts thatare not already required for operation with liquid-petroleum gas are theelectrical heater elements. In addition only the main switch need bereplaced with a converting switch.

The advantages achieved with the invention consist mainly in thefollowing points, taken together or separately:

Reduction of the investment in the heating-device inventory of abusiness by a fewer number of devices.

Reduction of the energy costs by simple changing of the form of energy,for example at the site, without switching the device.

Easy adaptation of the heater to the site requirements or otherrequirements.

More use of the individual device which can be employed in differentsituations.

Increase of safety by the greatly simplified possibility to switch toelectrical operation without an open flame.

Increase of the operational readiness and safety by improving theignitability when using oil or gas.

BRIEF DESCRIPTION OF THE DRAWING

The invention is more closely described with reference to the drawing inwhich by way of example a portable liquid-petroleum gas/electric hot-airblower is shown in a schematic longitudinal section.

SPECIFIC DESCRIPTION

The portable liquid-petroleum gas/electric hot-air blower shown in thedrawing has a tubular housing 1 that is provided with a carrying handle2 and with a bottom housing 3 formed as a control and connection box.The tubular housing 1 holds a combustion chamber 4 which is protectedfrom contact by a front protective mesh 5 and a back protective mesh 6.Behind the combustion chamber 4 is a fan 7 which is driven by a fanmotor 8 and which moves a controlled amount of air in the direction ofthe arrows through the housing 1. The combustion chamber 4 holds aburner plate 9 on which a gas burner 10 is provided. The gas burner 10is ignited by an ignition electrode 11 when gas is released. Thecontinuous burning of the flame is monitored by a flame detector 12which can be constituted as a photoelement, photoresistor,thermoelement, or ionization electrode. In case of a disturbance themonitor 12 stops the gas feed. A safety thermostat 13 shuts off the gasfeed in case of an excessive temperature increase with restricted airthroughflow or a defect of the fan 7 or of its motor 8. Between the fan7 and the gas burner 10 is an electrical heating element 4 that in theillustrated embodiment is formed as two planar wound tubular heatingbodies. A controller 15 mounted in the bottom housing 3 is connected tothe gas burner 10, the electrical heating element 14, the flame monitor12, the safety thermostat 13, and the fan motor 8.

I claim:
 1. A portable hot-air blower for at least two of the threeforms of energy including oil, liquid-petroleum gas, and electricity,the blower comprising:a tubular or tunnel-shaped housing defining acombustion chamber; blower means in the housing including a fan and afan motor for directing a current of air along an axis through thechamber; at least two heat sources axially spaced in the chamber in thehousing from one another, one of the heat sources being powerable byelectricity and the other of the heat sources being powered by arespective one of the other two forms of energy; an ambient-temperaturesensor; and control means connected to the sensor for, on detecting avery low ambient temperature, first operating the electrically poweredheat source until the blower is warm enough for safe operation of theother heat source and then operating the other heat source.
 2. Theportable hot-air blower defined in claim 1, further comprisingsensormeans for detecting a failure of operation of the heat sources; andcontrol means connected to the heat sources and to the sensor means for,on detected failure of one of the heat sources, switching from thefailed heat source to another of the heat sources.
 3. The portablehot-air blower defined in claim 1, further comprisingcontrol meansconnected to the heat sources and to the fan motor for varying therotation rate of the fan motor in accordance with which of the heatsources is being used.